From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Howells Subject: Re: Union mount and lockdep design issues Date: Wed, 13 Jul 2011 13:02:05 +0100 Message-ID: <30216.1310558525@redhat.com> References: <87tyar6gv8.fsf@tucsk.pomaz.szeredi.hu> <1310305703.13309.7.camel@twins> <4E0AF2BA.2040706@gmail.com> <1302756608.2854.10.camel@perseus.themaw.net> <4DA4B6A8.7030804@gmail.com> <4DA5DCB8.3040101@gmail.com> <4DA5F569.9020309@gmail.com> <24792.1302808448@redhat.com> <2477.1309342656@redhat.com> <4E1962BE.8010204@redhat.com> <1408.1310382069@redhat.com> <1310385651.18678.59.camel@twins> <1310392232.4276.14.camel@perseus.themaw.net> <1310 405033.4276.28.camel@perseus.themaw.net> Cc: dhowells@redhat.com, Michal Suchanek , Ian Kent , Peter Zijlstra , Ric Wheeler , Alexander Viro , Christoph Hellwig , Ingo Molnar , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Moyer To: Miklos Szeredi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:9374 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750785Ab1GMMCf (ORCPT ); Wed, 13 Jul 2011 08:02:35 -0400 In-Reply-To: <87tyar6gv8.fsf@tucsk.pomaz.szeredi.hu> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Miklos Szeredi wrote: > Overlayfs never locks both upper and lower at the same time, which means > there's no AB-BA locking dependency. The lock orderings are: What you're talking about is not analogous to the situation I'm seeing with unionmount. You actually have three filesystems in overlayfs. The interaction between overlayfs-and-upperfs and overlayfs-and-lowerfs is the equivalent in unionmount terms to upperfs-and-lowerfs. This is where the lockdep issue lies. David